Universal Constants
by BookkeeperThe
Summary: The BAU is asked to consult for UNIT, and find themselves working with a man whom even they have difficulty reading. Incredulity, distrust, and an excess of over-enthusiastic geniuses ensue. Teamfic, gen.
1. Chapter 1

**1) While I usually write for Doctor Who and have tried to make this accessible for members of both fandoms, this is from the BAU's point of view, so it probably helps to have seen at least a couple episodes of Criminal Minds. **

**2) To preserve the integrity of both canons, this assumes that the Doctor's universe has an alternate BAU which is essentially the same but exists in a world with the Battle of Canary Warf, etc, and no BBC show called Doctor Who. **

**3) Set after Journey's End for the Doctor, and shortly after Memoriam for the BAU. That means no JJ, which is unfortunate, but that's the way the timelines worked out.**

**4) I own neither Doctor Who nor Criminal Minds.**

**-BAU-**

Supervisory Special Agent Aaron Hotchner was not a superstitious man. He _did_, however, have enough sense and experience to know that certain things did not bode well for the near future. Calls from blocked numbers were disquieting. Haley waiting for him with crossed arms and a tapping foot was nerve-racking. Any member of his team coming to him with an expression which said "please don't kill the messenger" was alarming.

Section Chief Erin Strauss waiting for him in his office was . . . worrying, with a dash of irritating. It didn't have the same undertones of mortal peril as many aspects of his job did, or the emotionally draining potentials of Haley's wrath, but it did mean bureaucracy and politics and a number of other headache-inducing things.

At least she wasn't alone, which meant that this probably wasn't part of her ongoing attempts to dismantle his team. There was another woman with her – mid-thirties, dark, short-cropped hair, a nose a Roman would be proud of, and a feminine figure which wasn't quite hidden by her military posture and unfamiliar uniform. Some foreign military, perhaps? There was something vaguely exotic about the olive tone of her skin and the shape of her eyes.

"Chief Strauss," Aaron greeted with a nod as he entered his office.

"Agent Hotchner," she returned, all stiff professionalism. "I'd like to introduce you to Captain Ruth Stewart. Captain Stewart, this is Aaron Hotchner, unit chief of the BAU."

"Pleased to meet you, Agent Hotchner," Stewart said, brisk but not unfriendly. Flawless English, no accent. Probably not foreign, then.

"And you," Aaron replied, accepting her firm handshake. Confident, in control, nothing to prove. Good.

"Captain Stewart is from UNIT," Strauss explained. "She has requested that the BAU consult on a case. I've agreed."

Aaron did his best to conceal his surprise. He hadn't thought that UNIT ever cooperated with other agencies, much less asked them for help – and for good reason.

"All due respect, Captain Stewart, we study _human_ behavior. Unless you have a personnel problem . . ." Though even then, he wasn't sure. Did UNIT employ aliens? Reid would know. He'd ask the young agent later.

"We have a human killer," Stewart stated. "Alien victims. Our usual methods are failing us – we were hoping that you could offer a fresh perspective. It's imperative that we put a stop to this before word leaks out to extraterrestrial population on a whole."

Aaron glanced at Strauss, and knew that it would not be wise to fight her on this. He turned his gaze back to Stewart.

"We'd be glad to help."

Well, Reid would be happy.

**-BAU-**

"_I don't believe that there are aliens. I believe there are really different people."_ – Orson Scott Card

**-BAU-**

Derek Morgan flipped through the file he had been given. He flipped through it again. He looked at his boss, who ignored him steadily. He flipped through the file once more, just in case he had seen wrong the first two times.

He hadn't.

No wonder Hotch had waited to brief them until they were all on the jet. He had probably been worried that they wouldn't agree to come, otherwise.

"You're kidding," said David Rossi incredulously, stating what they were all (with the possible exception of Reid) thinking. "Aliens?"

"It's not exactly a foreign concept," said Hotch, who had obviously had plenty of time to come to terms with this himself. "Not like it would have been a few years ago. None of us can deny that they exist, or that they visit Earth."

He was right, of course. What with Canary Warf and President Winters' assassination and the latest event which had come to be known as "the Stolen Earth Incident," it had become common knowledge that aliens not only existed, they were advanced and ruthless and damned terrifying. Suddenly every law enforcement agency was giving lectures on how to recognize possible alien activity, and some of the more progressive colleges and universities were offering courses on xenobiology and the like. Still . . . .

"Hotch, this is insane. We don't know anything about aliens. _Most_ of us don't know anything about aliens," he clarified quickly, as Reid opened his mouth. Dr. Spencer Reid was a genius, with several PhDs at the ripe age of twenty-seven, and seemed to know everything about everything.

"We'll learn," said Hotch. "At the moment, we're assuming the unsub is human, and a member of UNIT, given his knowledge. It's a case just like any other." If he doubted his own words, he gave no outward indication. "He seems to have access to UNIT's records and has been targeting relocated extraterrestrials in the LA area. Specific cause of death hasn't been determined, but there are small puncture wounds in the necks of each of the victims. I think it's safe to say that they were all injected with a toxin of some sort."

"Okay," said Emily Prentiss. "So we start with victimology."

"They're all aliens," said Derek. He was stating the obvious, but that was part of the point of these discussions. A lot of the time it was something painfully simple which cracked the case.

"Could be a hate crime," Prentiss suggested.

"Could be," Hotch agreed, "but let's not get ahead of ourselves."

"They're not just aliens," said Reid. He was flipping through the crime scene photos, but Derek was sure that it was more to have something to do with his hands than because he really needed to look at them again. Photographic – oh, sorry, _eidetic_ – memory and all that. "They _look_ alien," the boy-genius continued. "None of them are humanoids."

"So?" asked Jordan Todd. She wasn't really a profiler; just the interim media liaison while JJ was on maternity leave, but it could be useful to get an outsider's perspective. "Couldn't it just be a coincidence? I mean, how many aliens look human?"

"You'd be surprised, actually," said Reid eagerly, sitting up a bit straighter. "A wildly disproportionate number of registered sentient species are externally similar to humans, some of them nearly identical, right down to the coloring. Xenobiologists call it parallel evolution, but there have been theories about a common ancestor; some ancient species which achieved interstellar travel millions of years ago but has since suffered some sort of calamity or simply devolved –"

"Alright, so not a coincidence," Derek said, cutting across the ramble before it could disintegrate into Star Trek references. "Could be that he can't bring himself to kill anything that looks human."

"It's possible," Hotch agreed.

"We know that unsubs dehumanize their victims," Prentiss remarked.

"The fact that these victims _aren't_ human would just make it that much easier," Rossi added.

"We need more information," declared Hotch. "Dave, when we land you go with Reid, Prentiss, and Jordan to UNIT headquarters. Talk to the experts; find out if there are any other commonalities between the victims. Morgan, you and I will go to the latest crime scene and a get a better grip on the methodology. There's more to this than meets the eye."

**-BAU-**

The crime scene was in an ordinary suburban neighborhood. It was the last place most people would have expected to house a reptilian refugee from the planet . . . something unpronounceable by humans. Which, Aaron supposed, was exactly why UNIT had chosen it for that purpose.

The entire street had been cordoned off and was crawling with UNIT personnel. Captain Stewart met them at the perimeter and waved them in.

"We had to clear the area of civilians, for security reasons," she explained as they strode towards a small, unremarkable house. "We interviewed them all, of course, but no one saw or heard anything. We've told them that there's a dangerous gas leak, and they've been given compensation." Her radio crackled.

"_Sergeant Jenkins to Captain Stewart, over."_

"Hang on a moment," said Stewart to Aaron, unhooking the radio from her belt. "This is Captain Stewart. Over."

"_Captain, we have a . . . we have a situation here at the crime scene. Over."_

"Explain, Sergeant. Over," said Stewart, coming to halt and holding up a hand for her visiting FBI agents to do the same.

"_We have a Code Nine."_

Complete and utter shock flashed across Stewart's face, and she nearly fumbled the radio.

"_Over," _Sergeant Jenkins (who sounded young and somewhat shaken) added belatedly.

"Did I here you correctly, Jenkins?" asked Stewart, quickly regaining her composure. "A Code Nine? _Here?_"

"_Yes, Ma'am. Right here in front of me,"_ replied Jenkins, taking his superior's lead and dropping the stiffly formal wording.

"Alright. I'll be right there," said Stewart, beginning to walk again with a new urgency.

"What does Code Nine mean?" questioned Hotch as he lengthened his stride to keep up.

"It means that the Doctor is here," said Stewart. She said the title like a name, and traces of excitement and fear showed through her professional mask.

"Who's the Doctor?" asked Morgan.

"If the stories hold true, then he's the smartest, bravest, best man you'll ever meet – and also the most dangerous."

They had reached the house. Stewart led them through the wide-open front door and into the kitchen, where a young man – presumably Sergeant Jenkins – hovered nervously, shifting his weight from foot to foot. He snapped to attention as Stewart passed.

"At ease, Sergeant," she said almost absently, not slowing down. She came to a halt as she stepped around the counter, and Aaron had to step to the side to see.

The first thing he noticed was the body. It was shaped like a human, to some extent, but clearly was not. The green scales which covered every visible inch of it made that obvious, not to mention the vicious looking claws and slit-like pupils in its yellow eyes. The face bore some resemblance to a crocodile's snout, but it was muted and softened, and no one could mistake the look of terror on the alien's face.

The second thing he noticed was the man crouched beside the body. He was wearing a brown, pinstriped suit under a long, tan trench coat, with incongruously casual converse. From this angle, most of his face was obscured by his artfully mussed brown hair. It took him a moment to register their presence, during which time he muttered to himself in a British accent – London, if Aaron was correct.

". . . but who would have that kind of knowledge? Well, Torchwood, maybe, but they don't go about assassinating peaceable aliens – well, not anymore, anyway – oh, hello!"

He sprung to his feet, grinning. His smile was wide and toothy and blinding, his movements bouncy and energetic. It was very, very distracting – intentionally so. His manner was perfectly calculated to draw attention away from the sharp glint in his dark eyes. Smart and dangerous, Stewart had said. Aaron believed it.

"Doctor," Stewart greeted briskly, snapping to attention and saluting.

"Oh, don't salute!" said the Doctor, cringing exaggeratedly – but while his dismay was overstated, it wasn't entirely manufactured. Interesting.

"Sorry, sir – Doctor," she modified, as he winced again. "I'm Captain Stewart, I'm in charge of this investigation. These are Agents Aaron Hotchner and Derek Morgan."

"Ah, yes, lovely to meet you," said the Doctor, shaking their hands with a firm and ice-cold grip. Despite his polite words, his smile became somewhat fixed and there was a touch of frost in his eyes as his gaze flickered to the guns on their belts.

"They're from the FBI's Behavioral Analysis Unit," Stewart elaborated.

"You're _psychologists_!" exclaimed the Doctor, his eyes thawing and his grin turning more genuine. "Oh, that's just brilliant," he continued. There was something slightly condescending in his delight. It was the same sort of tone that one might use when praising a particularly clever dog. "I love psychologists. Well, most psychologists. Well, I say 'most' . . ."

"Have you been briefed, Doctor?" asked Stewart, regaining the Doctor's wandering attention.

"Ah, yes, Leroy here was just explaining," said the Doctor, rocking back on his heels and nodding at Sergeant Jenkins, who looked more than a little terrified at being pointed out. "He hadn't quite gotten to the specifics, though. This would be . . .?"

He gestured to the body, reminding everyone of why they were there. Jenkins handed Stewart a file, and she began to explain to both the Doctor and the FBI agents, speaking over the sharp buzz of some device which the Doctor was running over the body.

"We called him Edward White; his birth name was . . . he wrote it down for us –"

The Doctor sprung to his feet, snatched the file from her hands, glanced at it, handed it back to her, and crouched down again, all in the space of about two seconds.

"It's pronounced" (He said something which involved several sharp clicks and sounded physically painful.) "No wonder he looks familiar," he commented, almost to himself. His manic energy had drained away, the darkness of his eyes spreading over his face and making him look very, very old.

"You knew him?" Aaron asked, a suspicion which had been tugging at the edges of his mind suddenly growing much more insistent.

"Well, in a way," said the Doctor with a sniff, recovering his bounce as he leaned back. "He arrested me once. Long time ago. He was just a kid, then. From" (He made another impossible sound.) "wasn't he? No, sorry, you'd call it Capella V."

"Um, yes," said Stewart, consulting the file. "He was one of the first individuals in our relocation program. He came here in the early eighties as a refugee when there was a revolution on his planet."

"I started that, I'm afraid," said the Doctor with a grimace. "It's a pity, really. He had potential – helped us escape. Well, Jack _said_ that he did. Personally, I'm don't think that letting Jack nick the keys off his belt while snogging the life out of him is quite the same thing – having the captain's tongue down your throat can be very distracting." The Doctor seemed to realize what he had just said, and cleared his throat uncomfortably. "Not that I'd know, of course."

"Of course," agreed Stewart, very carefully not amused. "I should inform headquarters of your arrival. The three of you feel free to look around; Jenkins will answer any questions you have. I'll be back a few minutes. Doctor. Agents."

She gave a sharp nod to each of them and departed.

The Doctor turned his attention back to the body. Aaron exchanged a glance with Morgan, who raised his eyebrow in an expression which clearly said _what the hell just happened?_ Aaron shook his head in reply.

"It's a crime scene. Treat it like one."

"Alright," said Morgan, and looked around, obviously struggling to fall back into familiar though-processes in such an unfamiliar situation. Aaron didn't miss the way the Doctor's posture shifted, or how his eyes tracked Morgan's movements with interest.

"The unsub came in through the back door," said Morgan, pacing over to the door and examining the lock. "Looks like he picked the lock without much trouble, so he's got some experience with breaking and entering. Probably has a criminal record." He moved over to the body, crouched down opposite the Doctor. "Do you mind?"

"Oh, by all means," said the Doctor, standing and stepping away with a sweeping wave.

"Puncture wound in the side of the neck, just like the others. This one's on the left, though, so assuming the unsub's right-handed that'd mean he was facing his killer. It looks like he saw what was coming."

"But none of the neighbors heard anything," said Aaron. "He was obviously frightened, so why didn't he scream?"

"Ah, I can answer that one," the Doctor interjected. "This species isn't capable of screaming. Haven't got the vocal chords for it. He wouldn't have been able to make a sound loud enough for the neighbors to hear, even he had the instinct to try."

"Right, Doctor . . . what was it?"

Morgan drew himself up as he spoke, his stance turning subtly confrontational. Classic alpha-male posturing. All of Aaron's education and experience told him that the Doctor (clearly an alpha personality himself) should have responded in kind. The fact that he didn't solidified Aaron's suspicions.

"Just the Doctor." No straightening of his spine, no instinctual attempts to look bigger – but the Doctor's grin went brittle and his eyes darkened in a way that Aaron wasn't entirely sure was figurative. Posturing of a different sort. Not all power was physical.

"So you're an alien expert?"

"More than that," said Aaron, by now quite certain. Cold skin, odd clothing, almost-not-quite normal reactions . . . and UNIT had a special code for his presence, for god's sake. "He _is_ an alien."

"_What?_" demanded Morgan, looking completely thrown.

"I am, actually, yeah," said the Doctor. He tried to sound casual, but Aaron could see him suppressing a flinch as Morgan recoiled. "Is that a problem?"

"Of course not," said Aaron, ignoring the incredulous look Morgan tossed him. Though their personnel were wary of him, UNIT obviously trusted the Doctor – indeed, Jenkins was quick to jump to his defense.

"The Doctor is a great ally of Earth, sir," said the young sergeant.

"Yes, exactly, thank you. Now, if we could get back to the matter at hand?"

"Yes, let's," agreed Stewart as she reentered the room. "What do you think of it, Doctor?"

"Well, the killer is definitely human, or at least very good at pretending he is. Picking locks, using needles for injection – any alien with the technology for interstellar flight would have more advanced tools."

"But?" Aaron prompted, feeling the weight in the Doctor's dramatic pause. The man certainly liked to put on a show.

"Buuuut," said the Doctor, drawing out the word, "he's not working alone. I can't get any reading at all on the poison he used, which means that whatever it is, it's either completely untraceable or metabolized almost instantly. That sort of thing, especially for a reptilian species, is way beyond human engineering capabilities in this century. There are only two people I know of with the knowledge to create something like that here and now, and one of them is in Cardiff. At least, I think he's in Cardiff."

His eyes went slightly unfocused for a moment, as if he was listening to something far away.

"Yep, definitely in Cardiff," he concluded with a nod.

"And who's the other?" asked Morgan.

"Me. And I wouldn't need to pick the lock; or use a needle."

The Doctor's tone was light, but there was no mistaking the expression in his eyes as he met Morgan's. It wasn't a challenge or even a threat so much as it was a warning.

_I am not soft; I am not safe. Dislike me all you want, but __**do not**__ get in my way._

For the first time since Aaron had met him, Morgan blinked first.


	2. Chapter 2

**Note: since people have been asking, I'd just like to mention: Captain Jack Harkness will not be physically present in this story. Given that he is, after all, Captain Jack Harkness, I can't promise that he won't manage to affect the plot anyway. ; )**

**-BAU-**

Derek stepped outside as he dialed, breathing in the fresh California air and trying to shake the unease which had settled in his chest. He had met several people who could chill him with a look; that went with the job. He had never expected to be on the same side as one of them.

The phone rang once, twice.

"_Emily Prentiss."_

"Hey, it's me."

"_Oh, hi. Look, I'm in the middle of something, can I hand you to Reid?"_

"Sure."

There were muffled voices and the sound of movement on the other end of the phone.

"_Dr. Reid."_

"Hey, kid. How's it going at Area 51?"

"_Pretty well, actually. Though, there are several key differences between UNIT and the legendary Area 51; for example, UNIT is international, whereas Area 51 –"_

"Is American. Yeah, Reid, I know." Half the time he wasn't sure whether the kid's sense of humor was honestly that impaired, or if he just enjoyed getting under Derek's skin. "Look, Hotch and I will be joining you guys soon, and we've got company."

"_What do you mean?"_

"Some expert of UNIT's just showed up out of the blue. An alien, apparently. He calls himself 'the Doctor.'"

"_Just 'the Doctor'?"_ asked Reid. There was a spark of excitement in his voice, and Derek could practically _hear_ his eyes shining with interest.

"Yeah. Why, what do you know about him?"

"_Not much – nothing definitive, anyway. There are hundreds of reports of him all throughout history, from all over the globe, but they're grossly inconsistent. The physical descriptions are all over the place, though he's always a Caucasian male, and thematically he's cast as everything from a messiah figure to a portent of doom."_

Only Reid, Derek reflected, could say the phrase 'portent of doom' with such delighted relish.

"All throughout history? So, what, it's a title that gets passed down?"

"_Probably not. For one, while his appearance changes, it doesn't do so in chronological order. There was one version of him who was purported to have been on Krakatoa shortly before the 1883 eruption, but_ _that same version was sighted at the launch of the Titanic twenty-nine years later, and in London during the Second World War, and at Downing Street just after that explosion a few years ago. And between all of this, there are about ten or twelve different versions of weaving in and out of history, from the Boston Tea Party to the Fire of London to the Great Depression."_

"Okay, so he's some sort of immortal shape-shifter?"

"_That's one theory."_

"Alright, spit it out," prompted Derek. He could almost feel the vibrations of suppressed excitement through the phone. "What do you think he is?"

"_The theory most frequently ascribed to is that he's a time traveler."_

"A time traveler," Derek repeated flatly.

If he hadn't already been convinced that this case was going to be completely insane, he was now.

**-BAU-**

Emily had been hearing about 'the Doctor' from everyone within earshot for the past fifteen minutes. So far, she had gathered the he was a genius (Spock and MacGyver and Holmes all rolled into one), an alien (one of those humanoids Reid had been talking about), and, above all, a hero.

"I mean, we do our part," one of the more enthusiastic speakers, a young agent named Curtis Wells, was saying. "But any really _big_ stuff – Canary Warf, or the Stolen Earth thing a few months ago – that's all him. Whenever we get in really over our heads, he's there, putting everything right again. There were even rumors about the whole mess with President Winters – I mean, he was definitely there, even if he didn't kill Saxon, but some people say it was way worse than it seemed. Like, something really, really horrible happened, but no one remembers because the Doctor _turned back time_."

Emily noted the way that one of the higher-ranking officers who had been listening in – the type who would probably have been privy to classified information – deliberately turned away and pretended to be busy with his computer.

Rossi gave a derisive snort.

"I don't buy it. If there were beings that powerful, why haven't they taken us over by now? Oh, this 'Doctor' is altruistic, sure, but a whole race?"

"But that's the thing, sir," said Curtis eagerly. "It's not a whole race. It's just him."

"What do you mean?" questioned Jordan, who was listening with mild skepticism and deep curiosity.

"Something happened to his planet, and everyone on it."

"What sort of thing?" asked Emily, drawn in despite herself. After all, if Reid believed it (and he clearly did, as he was soaking in every word in reverent and unprecedented silence), there had to be _some_ grain of truth to it . . . .

"No one's sure," said Curtis with a shrug. "We only get bits and pieces, after all. Whenever he shows up it's usually a crisis, so no one's really taking notes. There are myths and stuff, though, y'know, from aliens we've interviewed, and they say that there was a war. A war that destroyed whole galaxies. And _some_ of them say –"

"That's quite enough, Private Wells."

Curtis paled dramatically, snapping to attention as Emily jumped and spun around. Behind her stood a stern woman in a captain's uniform, glaring at Curtis, Hotch, carefully poker-faced, Morgan, trying to hide his disconcertion less successfully, and a man whom Emily assumed was the Doctor, rocking back on his heels with his eyebrows raised.

"Yes, Captain Stewart, Ma'am," said Curtis hastily, while the small crowd which had accumulated scattered. "Sorry, Ma'am."

"It's not me you should be apologizing to."

"Right." Curtis swallowed hard and turned to the Doctor, not quite managing to meet his eyes. "Sorry, sir."

"Oh, not at all," the Doctor responded cheerfully. He bounced around Captain Stewart and perched on the edge of a desk, clapping Curtis on the back. "Nothing like a bit of office gossip to pass the time, and let's be honest, I'm much more interesting than whoever's been nicking Jerry's stapler."

He grinned widely.

Jordan cleared her throat and stood, extending a well manicured hand.

"You're the Doctor, I'm guessing?"

"That's me! And you must be the rest of the BAU."

"That's right. I'm Agent Jordan Todd, media liaison. These are Supervisory Special Agents David Rossi, Emily Prentiss, and Dr. Spencer Reid."

"Oh, a doctor? What of?"

"Quite a few things, actually . . ."

The Doctor was a bit like Reid, Emily noted, watching the supposed alien's grin widen a bit more with every degree the boy-genius listed, all tall and gangly and over-enthusiastic, chattering on about particle physics and historic FBI agents and remaining completely oblivious to Curtis' discomfort and Rossi's distaste.

Check that, he was a _lot_ like Reid, when she looked closer. He was unhealthily skinny and a shade too pale, giving off the same, faint aura of exhaustion and abandonment which their youngest team member did on his rougher days.

His whole planet was gone, Curtis had said. She couldn't even begin to imagine it.

"Alright, we can chat later," said Hotch abruptly, cutting through the conversation. "Right now we have a killer to catch. Did you find any further connection between the victims?"

"We did, actually," said Emily, snapping back onto topic. "Reid was right when he said that none of them are humanoid, but there's something else as well. All the victims come from societies which are significantly more technologically advanced than humans."

"Let me see," requested the Doctor, accepting the files from Jordan and flipping through them even faster than Reid had.

"So what does that mean?" asked Morgan.

"The unsub is taking out aliens whom he believes are a threat?" suggested Hotch. "He could view himself as some sort of freedom fighter."

"They're not people whom _he_ feels threatened by," said the Doctor. His bright, cheerful energy had drained away, but there was still a certain sharp-edged enthusiasm in his eyes.

"What do you mean?"

"You remember how I said he wasn't working alone?" he asked, and then continued without waiting for a response. "Every single one of these people had at least level 2 technology. Usually, that means Smart Security – systems which automatically scan for threats in the vicinity and which can see through most cloaking devices. Planets which have it put it in everything from microwaves to remote-control toys. Someone out there is doing something which they don't want anyone to know about."

"That would explain the missing items," said Curtis, and then swallowed hard as everyone's attention turned to him. "There were alien devices missing from every home – things the victims had with them when they came here, or which we had recovered from other crash sites."

"That's right; someone mentioned that," agreed Rossi. "We assumed that they were being taken as trophies."

"More likely they contained some sort of alarm which would have alerted this lot that something was wrong," said the Doctor, gesturing widely to indicate UNIT as a whole.

The phone rang, and they all jumped. Captain Stewart picked it up, her face turning, if possible, grimmer.

"There's been another killing."

**-BAU-**

"_Temple of Benevolent Omniscience, home of the omnipotent High Sorceress of Technology, speak and be answered."_

"Hey, Baby Doll," Derek greeted warmly, a grin finding its way onto his face despite it all. Penelope Garcia, colorful technical analyst, tended to have that effect on people. "Do you have access to UNIT's files?"

"_I sure do. All things extraterrestrial are at my command. What does my hunk of burning love want today?" _

Derek glanced around to make sure that he was still alone in the secluded hallway he had retreated to. The Doctor was with Prentiss and Jordan at the crime scene, but he doubted that Hotch would approve of what he was doing, either. Normally that may have stopped him, but in this case . . . something was seriously Not Right, and he was going to find out what.

"Could you access the files on an alien called 'the Doctor'?"

"_Coming right up, hot stuff. Searching for 'the Doctor' . . . sorry, no can do. His files are sealed."_

"So unseal them."

"_If only it were that simple. They're not sealed by UNIT – they're sealed by __**Torchwood.**__"_

"What's that?"

"_No one knows,"_ said Penelope, in a dramatic stage whisper. _"Some super-mysterious British organization, beyond top secret. There are all these conspiracy theories about religious orders and ghost busters and time travelling immortals and stuff, but no one knows for sure. Point is, when they seal something, it's sealed."_

"I thought you were the omnipotent sorceress of technology," said Morgan, half teasing, half disappointed.

"_Nearly omnipotent. This is duct tape, crazy glue, peanut-butter-on-the-roof-of-your-mouth sealed. Think the Pentagon, plus the CIA, times Area 51."_

"Okay, sealed is sealed. I get it."

"_No, I don't think you do. Torchwood is like, the Pharaoh's Curse of hacking. People who try to hack them wake up the next day with no memory of the night before and nothing but gay porn in their hard drive."_

". . . you're serious?"

"_Deadly. It happened to a friend of mine."_

"Right. Well, thanks for trying."

"_Anytime, darling. Garcia out!"_

The line went dead. It was a moment before Derek tucked his phone away, lost in thought as he was. The Doctor wasn't just dangerous in and of himself – he had dangerous friends. Dangerous, powerful friends, with a skewed sense of humor.

The more he learned, the more he was certain that the BAU was in way over their heads.

"Morgan."

He jumped and spun around, biting back a curse. _Damn_, but Hotch walked quietly.

"Hey, Hotch. Something wrong?"

"Not on my end."

Hotch held his gaze. Derek stubbornly said nothing.

"You have good instincts, Morgan," said Hotch at last. "Right now they're rebelling against the fact that the Doctor isn't human, and that's perfectly natural, but he's on our side. More than that, he's a good man, and we owe him our respect."

"'_We owe him our' – ?_" Derek sputtered incredulously. "Dammit, Hotch, we don't even know him!"

"No, but UNIT does," Hotch replied evenly. He stepped back, pointedly clearing the way back to the UNIT bullpen. "We're not going to accomplish anything without the Doctor's expertise; we have time. Why don't you listen to what they have to say?"

Derek sighed inwardly, and conceded. Hotch obviously knew something he didn't, and he could usually trust his boss's judgment.

"Alright."

Captain Stewart already had a file up on a computer when he stepped into the bullpen. Obviously Hotch had let her in on his plan.

"This is an interview with one Mr. Copper," she said, stepping back and allowing him to sit at the desk. "He's a gentleman from the planet Sto who appeared in England last Christmas with nothing but the clothes on his back and one million pounds. This is his account of how he came to be there."

Morgan began to read.

**-BAU-**

"If you're an alien, why do you have a British accent?"

Emily suppressed a grin at the bewildered expression that flashed across the Doctor's face as he twisted in the passenger seat to look at Jordan, who was leaning forward as she questioned him.

"What? Oh, that. It's just where I spend most of my time, that's all."

"Why?"

"It's where I ended up when I first came to Earth," said the Doctor with a shrug. His started out slowly and picked up the pace as he continued speaking – Emily was sure that he was making it all up on the spot. "I got a bit addicted to the tea, you see. They make wonderful tea, the British. Not that the States haven't got their attractions – you've got beautiful landscapes, fascinating people, and believe me, I'm all for democracy – but you can't get a good cuppa to save your life."

"You sure it wasn't the emotional repression which made you feel at home?" asked Emily teasingly. In the short time since she had met the Doctor she had already seen enough to know that, beneath his wide smile and his charm, he was reticent to the extreme when it came to his true feelings.

"Now, don't go profiling me," said the Doctor, and while his voice was still light and friendly there was a hint of real warning beneath it. "I'm not one of your unsubs."

"Sorry," she replied, glancing sideways at him. He was looking out the window, but whether he was actually interested in the view or just avoiding her eyes was difficult to tell. "I'm surprised our techniques even work on you," she said, changing the subject. "Since you're an alien, wouldn't you have an entirely different psychology?"

"We-ell," said the Doctor, shifting his attention back to her and lighting up again, "I'm a bit of a special case. Spend nine hundred years saving one planet and you're bound to pick up some of their customs."

His hand went to the back of his neck when he mentioned his age, a typical gesture of discomfort. Emily would have almost said he was lying, except – he was at _least_ that old, according to UNIT. So, what, the other way? He was actually older, pretending that he was barely under a millennium?

Men and their vanity. Maybe aliens weren't so different after all.

"You're right, though," said the Doctor, shaking her out of her thoughts. "I am a different species, and that impacts a lot of things. My physiological reactions would be different, for example. I have much better control, when I choose to, over everything from micro expressions to respiration. I'm much more intelligent, obviously –"

"Obviously," Emily agreed, deadpan, while Jordan gave a snort from the backseat.

The Doctor ignored them.

"—and I have a few more senses and a significantly different cultural background, so that changes things. Still, most humanoid species have similar emotional cues, and all sentient species have the same basic needs and desires. Nourishment, shelter, security . . ."

"Sex," Emily interjected.

"Well, companionship, usually, but not necessarily sex. There are quite a few asexual beings in the Universe."

"Are you one of them?" asked Emily, with just a hint of flirtation, half-hoping to fluster the over-confident alien.

The Doctor responded with a raised eyebrow and a sidelong glance.

"Depends who's asking."

"Oh, I see how it is!" Emily laughed, while they pulled into the driveway of the latest crime scene and Jordan made a startled, amused sound from the backseat. "Time-travelling alien genius my ass; men are all the same."

"Remind me never to introduce you to Captain Jack," said the Doctor as they rolled to a halt.

Their banter died away as they climbed out of the car and entered the house. The private who was standing in the doorway of the living room gave them a grim nod and stepped aside. They entered the room – and came to halt as they caught sight of the small, crumpled body.

Jordan let out a soft 'oh,' bringing her hand up to cover her mouth. The Doctor's jaw clenched, his eyes going very dark. Emily felt her eyes sting as bile rose in her throat.

It was a child.

An alien child, obviously, with cat-like ears, peach-fuzz fur, and a small (probably vestigial) tail – but still a child, all wide eyes (now glazed and blank), round features (now eternally frozen), and delicate limbs (now twisted in an unnatural position where he had fallen).

The Doctor was the first to move, crouching beside the body and examining it with a painfully compassionate gaze which couldn't quite mask the fury in his eyes.

"What was his name?" he asked, soft but unyielding, velvet over iron.

"His real name was Thamil, but we called him Timmy," said the private. "It's a shame – he was a sweet kid. His family crashed here about six years ago; he was just a baby. His dad didn't make it, so it was just him and his mom. He gave her no end of trouble – didn't understand why he had to wear a perception filter around his friends; kept wanting to show off his tail."

"His mother?" Emily questioned.

"Dead also, upstairs," said the private. "She fought back – looks like she didn't realize what had happened to her son. Small mercies, right?"

"She fought back? Is there any of the unsub's DNA?" asked Emily, with a spark of hope. Profiles were all well and good, but hard evidence made their jobs a _lot_ easier.

"The techs are working on it. It's a bit hard to untangle it from hers, what with her being alien and all, but we've gotten pretty good at that sort of thing."

"She didn't realize?" said the Doctor from where he stood, still frowning at the body.

"No, sir," the private responded. "She was still folding laundry when he came up behind her. It was just luck that she turned around in time to take a bite out of the bastard."

"Was she injured in the crash?" the Doctor asked, shifting his gaze and the full weight of his attention to the private. "Head trauma, anything?"

"No, sir. She was rather hysterical, understandably, but physically unharmed."

"Why do you ask?" asked Jordan.

"Because Lutarians – that's their species – they're empathic. They can feel other people's emotions," he elaborated, at Jordan's blank look. "Any healthy Lutarian would have known the instant anyone entered their house, especially anyone with murderous intent. Unless . . ."

He trailed off, frowning into the middle distance.

"Unless?" Emily prompted after a moment.

"Unless they were psychically shielded!" said the Doctor, spinning around with startling suddenness and gesturing sharply with the hand which wasn't tucked into his pocket.

"What does that mean?" asked Emily.

The Doctor grinned in response, toothy and wild-eyed.

"It means, Emily Prentiss, that I know what we're dealing with."


	3. Chapter 3

**Notes: Sorry about the wait on this one. As some of you may know, I don't often do stories with quite this much plot. I'm finding it an exciting challenge. Now that I've gotten past most of the exposition (and RL has settled down), it will hopefully go a bit faster.**

**-BAU-  
**

Morgan looked slightly stunned as he pulled away from the computer, and Aaron didn't blame him. He had had a similar reaction after reading the story, and Dave had muttered about finding something stronger than coffee before moving off to collect his thoughts.

It was an incredible story – the story of an old man with a young face and sad eyes who faced fearsome enemies with nothing but his wits and a screwdriver; of a stranger and a stowaway who saw off the ghost of a girl he barely knew with a kiss and a kind word; of a genius and a hero who saved six billion human lives and three alien ones (and his own, though it was obvious even from Mr. Copper's muddled account that the Doctor viewed that as next to nothing) and walked away with nothing to show for it but a fresh loss and the admiration of an old fraud.

The story didn't show that the Doctor was safe, or even stable – quite the opposite, in fact. If he had been one of Aaron's agents, he wouldn't have been allowed in the field, what with his god complex as his death wish. But the fact remained that he _wasn't_ one of Aaron's agents, nor could he be held to human standards for psychological health. The story _did_ show that the Doctor was . . . not kind, necessarily, but benevolent.

And while Aaron would be keeping a very close watch on the Doctor's recklessness and his penchant for nearly suicidal self-sacrifice, those traits were exactly the sort of thing which would win Morgan's respect.

"Alright, one question," said Morgan, addressing Captain Stewart, who nodded her assent. "What's Torchwood, and why have they sealed the Doctor's files?"

Thankfully, Captain Stewart didn't look offended by the implication that Morgan had been poking around behind her back. Instead she just sighed, her military posture slumping slightly and her expression shifting to vague irritation at something which wasn't there.

"You realize that everything you learn over the course of this investigation is highly classified?" she asked, in the slightly bored tone of someone who was required to say this.

"Sure," Morgan agreed.

"Torchwood is a headache. It's a secret organization founded over a century ago to protect Great Britain from aliens. Most of it was destroyed in Canary Warf, but there's a remnant left in Wales – they have very fancy toys, a lot of nerve, and no rules. They're also occasionally helpful, so we try to live and let live."

"What does that have to do with the Doctor?"

"The head of Torchwood is a personal friend of his. He wanted to put some extra security on his files, to make sure that no sensitive information got into the wrong hands. We agreed – we still have access to them, obviously, and additional security is never a bad thing, especially when it comes to the Doctor."

Speaking of doctors . . .

"Where's Reid?"

"Over at the evidence board, I think," said Derek, gesturing vaguely over his shoulder. He continued his conversation with Captain Stewart as Aaron walked out of earshot. "So, how'd something like Torchwood stay under the radar? You'd think that with all the press aliens are . . ."

Reid was indeed at the evidence board, a cup of coffee in hand and a frown on his face. He seemed to be lost in thought as he stared at the crime scene photos, and he didn't notice as Aaron came up behind him. The unit chief took a moment to observe his youngest agent – he was looking slightly worn, as was to be expected after the difficult events of the past couple weeks, but overall he seemed to be holding up relatively well. There was no defensiveness in his posture, no tell-tale trembling in his fingers. He wasn't backsliding; the rest would just take time.

"What do you see?" asked Aaron at last.

"I'm not sure, yet . . ." said Reid, his frown deepening.

"Keep working on it," said Aaron, knowing that the young agent would do so anyway, and also knowing that he needed the reassurance of his superior's approval, now more than ever.

"I will," Reid replied absently, his mind already back on the case. Aaron left him to it, glancing at his watch as he did so. Prentiss, Jordan, and the Doctor would be back soon, hopefully with new information.

With any luck, this case would be wrapped up quickly.

**-BAU-**

Spencer _almost_ had it. He could feel it, the clarity, the revelation, hovering right at the edges of his mind, just out of reach. There was something he was missing, something they were all missing, something just – about – _there_ –

The Doctor's arrival derailed his train of thought.

It wasn't a loud arrival, or a violent one, or even particularly unusual – the Time Lord simply walked through the door, Prentiss and Jordan trailing behind him. But still, the instant he stepped into the room, everyone's eyes were on him. Spencer wasn't sure what the other, more aggressive people were feeling, but for his part there was something tingling up his spine, making the hairs on the back of his neck stand on end and whispering a single word in his ear.

_RUN._

He clamped down on the fear even as he identified the cause: the Doctor wasn't playing human anymore. Something had shifted in his expression and his posture, some façade had fallen away, and now every one of Spencer's instincts, primate to profiler, recognized him as an alien, and a predator.

"It's a Phantom Assassin," the Doctor stated in the suddenly silent room.

Predictably, it was Hotch who first dared to attract his attention by speaking.

"What does that mean?"

"They're part of a telepathic race called the U'ulau. They're symbiots – they have no corporeal form, so they hitch a ride with the other sentient species on their planet. Usually, that works fine, but in certain situations the U'ulau can get dislodged. They can make do with other species for a while, but if they're without a proper host for too long it . . . twists them."

There was a tension in the Doctor's jaw and a darkness in his eyes which spoke of more than academic knowledge. Spencer wondered whether it was some residual trauma from a past encounter with these 'Phantom Assassins,' or a more personal understanding of what isolation did to telepaths – or to anyone, for that matter.

"How so?" asked Rossi.

"It damages their moral compass. Turns perfectly healthy individuals into psychopaths. Thing is, U'ulau are clever – they don't just go about offing whoever they feel like, hence the Phantom Assassins. That's what they call themselves, anyway – 'hit men' is probably a more accurate term. They team up with corporeal beings, sometimes other criminals, sometimes just innocents whom they've manipulated, and use their telepathic and technological abilities to kill for profit."

"So that's what this is all about?" asked Stewart. "The victims all have hits out on them?"

"No." The Doctor had paced his way into the bullpen as he spoke, but now he stopped, gripping the back of a chair with white knuckles. "There's a reason that the Phantom Assassins are the most expensive contract killers in the Universe. They make absolutely sure that their target is dead – by blowing up their ship, or their home, or, on less developed worlds like this one . . . their planet."

A ripple of shock and fear went around the room, and Spencer felt his insides freeze. He wasn't entirely unfamiliar with the concept of imminent planetary destruction – no one was, these days – but he remembered the helplessness of it, the terror and confusion of jerking out of a trance to find himself on the edge of a roof (with no one begging him to come down), the foreign feeling of utter ignorance as Daleks swarmed the streets, the sick guilt and loss and anger which mingled in his stomach when he finally tracked his estranged father down, only to find that he had been exterminated months ago . . . .

But they weren't helpless, this time. They had an ally who was, according to rumor and legend, far more fearsome than anything else the Universe could produce.

Meeting the Doctor's eyes, ancient and dark and filled with slow-burning fury, Spencer was willing to trust in rumor and legend.

"How?" he asked, slightly choked, more than slightly high-pitched. He didn't think that he could force out the rest of the question – _How could one man, highly advanced alien or not, destroy a __**planet?**__ –_ but fortunately, the Doctor seemed to understand him anyway.

"That's the thing!" said the Doctor, spinning into motion again as he slipped on a pair of thick-framed glasses, darting over to a computer and pulling out some device – his sonic screwdriver, if memory served correctly (and Reid's always did, except when trauma and time and certain genetic predispositions meant that it didn't). "It shouldn't be possible!

"Oh, there are plenty of ways to blow up a planet," he continued over the buzz of his screwdriver, waving his free hand in a dismissive gesture. "But we're not near any Rifts, and most others require drilling into the core, and even you lot would have noticed that." He stopped suddenly, reconsidering his words.

"There _haven't_ been any unusual earthquakes lately, have there?" he questioned, shooting a glance over his shoulder.

"No," answered Stewart, her voice dry as a desert.

"Right, then," said the Doctor, oblivious (or rather, Spencer thought, pretending to be oblivious). "Meteorites would work too, or just one, if it were big enough, but then the U'ulau wouldn't have needed to land, even, much less settle in and start knocking off threats and _I can't get a fix on this bloody signal!_"

His sudden increase in volume was accompanied by an ineffective smack to the computer he was working on, and everyone around him jerked backwards in alarm.

"Sorry," he said, visibly reigning in his temper. He pulled his glasses off and pinched the bridge of his nose, squeezing his eyes shut as he leaned heavily against the desk.

"Alright!" he said abruptly, straightening with another surge of energy. "He's using some sort of cloaking device, and a good one, too. Regulan, probably. I won't be able to track the signal back to his location, but I can tell that he's sending one out."

"But what for?" asked Morgan, who had been unusually quiet up to this point – his initial suspicion seemed to have faded, but there was still a wariness about the way he eyed the Doctor from a distance.

"If my guess is right – and mine usually are – bombs. A whole grid of them, all very powerful, set at key locations on the Earth's surface. It wouldn't be hard to set up, with the sort of budget and technology which he's probably working with.

"What I can't figure out," the Doctor continued, turning on his heel and beginning to pace again, frustration and restlessness rolling off of him in waves, "is how he thinks he's going to get the signal to all of them at once. They'd have to go off within nanoseconds of each other for his plan to work; otherwise he'd trigger all sorts of safeguards and security systems. He'd have to relay the signal to the whole planet at once, and that's incredibly difficult, even from orbit. It _definitely_ shouldn't be possible from the planet's surface."

"Could he use satellites?" asked Prentiss.

"Well, yes, in theory, but he'd need a worldwide system, and with the intricacy of the signal it would need to be fully compatible on every level. Earth's never had anything like that – well, except for the Archangel Network, but that's been dismantled."

"No, it hasn't," stated Spencer, reflexively correcting false information. He was completely unprepared for the Doctor's reaction.

The Time Lord went rigid and white as a sheet, eyes wide, pupils dilated – he physically stopped breathing for one beat, two, and then –

"What?" he questioned, breathing steady again and voice deadly calm.

"The network was shut down, but the satellites were never decommissioned," said Spencer, responding automatically even as his mind raced – that had been a fear response, quickly controlled. Pure terror, almost instantly recognized as irrational and suppressed. An old memory, a nightmare – Harold Saxon had been key in the construction of the Archangel Network, Spencer recalled. And Private Wells had said that something terrible had happened, something which Saxon was involved in, something so horrific that even a man who had survived the death of his planet couldn't bear to let it stand –

The Doctor's voice, quiet and venomous and hard as steel, cut through his thoughts.

"I told you," he growled, turning to glare at Captain Stewart with eyes like black holes, "to rip those satellites out of the sky. I told you to tear them into lots of little, tiny pieces, and melt the pieces down, and throw the scraps in the deepest, darkest pit you could find."

In Stewart's place, Spencer was quite sure that he would have been stuttering excuses and babbling about how it hadn't been his decision. She was apparently made of stronger stuff, however, because she held her ground.

"There's been talk of repurposing them. The British government poured billions of dollars into that technology –"

"_The Master_ made sure that the British government poured billions of dollars into that technology," the Doctor ground out, teeth bared, "and whatever propaganda your superiors have been spouting, that technology is not the product of human engineering. It is far beyond your comprehension; you had _no right_ –"

"Alright, enough." Hotch's voice cut across the Doctor's, his even tone a sharp contrast to the alien's quickly-fraying control. "Jurisdictional battles can wait."

"That's not – I –_ jurisdictional – ?_" the Doctor sputtered, but Hotch cut him off with a glare.

"_Right now_ we have an apocalypse to avert. Assuming that the unsub is using the Archangel Network, can we stop the signal?"

"Yes, of course," said the Doctor, suddenly business-like again in another whiplash mood swing. His human mask was back, his power and his emotions under tight guard once more. Anyone could have passed him on the street and had no idea who or what he was. The change was abrupt, startling, and somehow more disturbing than its inverse.

"I know that network like the back of my hand," he continued. "Give me access to UNIT's systems and the signal will be dead before he even has a chance to finish calibrating it. The real problem will be tracking him down. Given enough time it wouldn't be a problem; but he'll be running far and fast as soon as he figures out that his little plot fell through, and I don't want to risk him coming in for a second attempt – which he will, more likely than not."

"So we track him through his host," said Hotch.

"We can build a profile around what you've told us," Morgan agreed. "Are there any specific behaviors which would point to whoever it's . . . possessing?"

"We-ell," said the Doctor, drawing out the word with a grimace and rubbing the back of his neck in a habitual motion, "it's not possession, really – more like cohabitation. An U'ulau can't overpower anyone's will, except the way any clever, insightful being can."

"Manipulation," said Rossi, giving the Doctor a piercing look.

"Precisely," replied the Doctor lightly, either missing or (more likely, in Spencer's opinion) ignoring the glance. "Though, humans aren't really meant for that sort of telepathic fusion any more than the U'ulau is meant to be living in a human mind. It won't do any permanent damage, but whoever's playing host to our Phantom Menace is bound to be distracted, and he'll probably have one hell of a headache."

"Right, I think that gives us enough to work with," declared Hotch, glancing around at Spencer and the rest of the team as if waiting for one of them to disagree. No one did. "Doctor, how quickly can this alien leave the planet once you cancel his signal?"

"Oh, what with noticing that his plan is shot, trying to fix it, failing, kicking things, and eventually giving up and clearing away the evidence . . . I'd say about three hours. Longer, if I can set up a general obstruction field to interfere with his equipment."

"Do that, as soon as you cancel signal," ordered Hotch.

The Doctor's eyebrows shot up, but thankfully he seemed more amused than affronted. Spencer did not relish the thought of getting caught in a collision between his immovable boss and the apparently unstoppable Doctor.

"Absolutely. You lot do what you do; I'll be finished before you can say 'my, but isn't that Doctor clever?'" He flashed a cheeky grin over his shoulder as he departed in a flurry of coattails.

It was indeed barely half a second (composed entirely of astounded silence) before he was back again, sticking his head through the doorway and looking slightly sheepish.

"Er, all the fancy computers would be where, exactly . . . ?"

Rossi gave a snort and Jordan made a choking sound, both of which the Doctor ignored.

"I'll show you, s – Doctor," offered Private Wells, stepping forward.

"Yes, thank you." The Doctor ducked out of sight again. "Oh!" he exclaimed as he popped back into view an instant later, making them all jump. "Spencer! You have a doctorate in mathematics. Can you do calculus in your head?"

"Uh, yeah," said Spencer, caught off guard. His voice was embarrassingly high-pitched, and he cleared his throat before continuing. "Yeah, I can do that, yeah." It had been a while since he had done anything beyond single variables with any sort of speed, but he was sure that he could manage it.

"Excellent! I need to borrow you for a bit. Allons-y!"

And he swept off again, Private Wells jogging to catch up.

Spencer glanced uncertainly at Hotch, who nodded.

"Go ahead," he instructed.

Spencer obeyed, trying not to think too hard about whom, exactly, he was following.

As always, Spencer found that no amount of willpower would keep his brain quiet.

The man he was following frightened Morgan. The man he was following found Hotch _amusing_, in the same way that a good-humored Great Dane would find a pushy Chihuahua amusing.

Most terrifying and liberating of all, the man whom Spencer was following was smarter than he was.


	4. Chapter 4

Spencer was, for once, struggling to keep up.

The Doctor had laid out 'a few of the simpler equations' for him and was now tossing out variables at sporadic intervals while his fingers moved with incredible speed over the keyboard. Presumably, he was doing the more complicated calculations in his head as he did so – and, at the same time, he was chatting easily with the technical analyst whose office they had invaded. She had looked quite irritated when they swept in an hour ago, but now she was flipping her hair and giggling girlishly at some joke of the Doctor's. Spencer, meanwhile, was entirely focused on returning accurate values when the Doctor asked for them.

He would have probably been envious of the Doctor's ability to instantly ingratiate himself into his surroundings if he hadn't recognized it for what it was – the survival mechanism of a man who constantly relied on the acceptance of strangers. The Doctor had to make it seem like he belonged everywhere, because he didn't _really_ belong anywhere.

There was a lull in the string of numbers, and Spencer's attention turned to the conversation which he previously hadn't had the spare brainpower to register.

"Oh my gosh, listen to you!" the technical analyst was exclaiming. "You are such a geek!"

"That I am," agreed the Doctor, ducking his head with false embarrassment. Or was it false? It was hard to tell what was real with the Doctor – he was like an optical illusion, shifting in impossible ways every time Spencer turned his head.

"Don't tell those guys," said the technical analyst, rolling her eyes and jerking her head towards the door, indicating UNIT's military personnel. "It will break their little macho hearts. They're all convinced that you're secretly some sort of action hero – god forbid that someone save the world just by being _intelligent_."

Something clicked in Spencer's brain.

"That's it!" he exclaimed.

"What?" questioned the Doctor, looking just as lost as everyone else did when Spencer spoke without explaining himself, but Spencer wasn't listening. He scrambled for the door, nearly tripping over his own feet in his hurry.

"He's not a soldier!" he said excitedly as he burst into the main room, the Doctor at his heels. "The unsub – he works for UNIT, that's how he got the records, but he's not a soldier."

There was a pause as everyone turned to stare at him, wearing nearly identical looks of incomprehension.

"Oh," the Doctor breathed from behind him, understanding. "He turned around."

"Exactly!"

"Wait, what?" questioned Morgan.

"Reid, explain," ordered Hotch.

"That reptilian alien –"

The Doctor made a sound which was presumably the alien's real name. Spencer didn't bother trying to replicate it.

"—he was in the middle of cooking his dinner; halfway through chopping an onion. Why would he have turned around?"

"Because he heard the unsub coming . . . and a soldier would have walked more stealthily," Prentiss said slowly, comprehension dawning on her face.

"Much more stealthily," the Doctor agreed. "That species has terrible hearing – they rely primarily on scent, and that would have been completely obscured by the onion."

"Alright, so he's a scientist or a technician of some sort," said Hotch. "That narrows it down."

"Not enough," said Captain Stewart with a negative shake of her head. "We have hundreds of people working here; almost half of them don't have military training."

"That's what the rest of the profile is for. We should be ready to present it fairly soon. Doctor, what progress have you made on those signals?"

"Oh, I'm done," said the Doctor cheerfully, rocking back on his heels. "The planet's safe – well, as safe as it ever is – and it should be a good, oh, six, seven hours before the U'ulau can get his ship off the ground."

"Good," was all Hotch said, but Spencer could see from the tension in his jaw that he would have liked longer. Even assuming that someone recognized the profile right away, they still had to track the unsub down, organize an assault team, travel to his location . . . six hours was enough time, if everything went according to plan; it even left some room for error, but not much.

Hopefully, everything would go smoothly.

**-BAU-**

Dave let the others present the profile, keeping his attention on the Doctor.

"The man we're looking for is a member of UNIT, but not of the armed forces. He has a criminal record, but given that he works here, it's probably been expunged."

To the alien's credit, he didn't seem to resent no longer being the center of attention. His magnetic quality wasn't something he exploited or worked at; he hardly even seemed aware of it. He also seemed genuinely interested in what the team was saying.

"The hours of the attacks mean that he has either recently quit or been fired, or, more likely, that he works some kind of night shift."

"You keep saying 'he,'" Captain Stewart interjected. "How do you know it's a man?"

"One of the latest victims was a child," explained Prentiss. "An alien one, but still humanoid enough to invoke maternal instincts. While it's not unheard of for women to kill children, it's usually a specific delusion or obsession which drives them to it. With this sort of task-oriented killing, women will almost always show mercy to children, if only to the extent of treating their bodies more respectfully after death. There was no evidence of that here."

There was a shift in the Doctor's expression as Prentiss spoke of the dead child, a hardening of his face and darkening of his eyes. Dave recalled how he had acted before the child was killed – casual and charming, interested in catching the killer but perfectly willing to take his time about it. Afterwards, though . . . .

Dave generally viewed intense anger as a sign of weakness. It meant that you weren't thinking straight; made you more likely to make mistakes. It was good in an unsub; bad in an agent; very bad in a leader. The Doctor had certainly shown touches of that rage, personal and pain-filled, when he had learned of the Archangel Network's continued existence, at it had been terrifying.

His cold, controlled fury at the mere mention of the dead child was worse.

"It's important to remember that while the human who is physically committing these crimes is working in collaboration with an alien entity, he is _not_ being controlled. Most likely he has suffered some recent loss or trauma that has caused him to lose faith in humanity, to the point where apocalyptic destruction is actually appealing to him."

"He could believe that humanity is irredeemably corrupted and needs to be put down, or even that he's doing the world a favor by putting it out of its misery."

The Doctor's eyes flickered away and down; a universal expression of shame. Perhaps he had had similar thoughts himself – about Earth, or his own planet, or maybe simply himself. The fragments of stories which Dave had heard had hinted at deep self-loathing beneath his arrogance.

"This man works here. Someone knows him. Think about anyone who's been acting oddly lately – not finishing their work, drifting off, seeming distracted or irritable. Especially concentrate on anyone who's undergone some sort of tragedy recently."

"Peter Thompson!"

Every head turned to the source of the voice, a plain, middle-aged woman in a lab coat.

"Sorry," she said, blushing. "It's just, Thompson – he's one of my lab assistants. He's been sloppy in the past few weeks, distant. I thought it was just stress . . . his wife committed suicide a couple months ago."

Everyone surged into action. Aaron barked for Thompson's personnel file; a technician, anticipating, already had it up on the screen; Stewart was calling for a team to be put together; the Doctor . . . .

The Doctor was pulling on his coat. He was expecting to go with them, Dave realized. Of course he was; he was used to being in the thick of things, but Aaron would put a stop to that quickly enough –

Except that he wasn't. Aaron was actually encouraging the Doctor, pulling him into the discussion of the most effective way to talk to the unsub.

"Doctor, we'll need you to try and communicate with the alien. You probably understand its psychology best. Meanwhile, we'll try to divide and conquer – we might not be able to restore Thompson's faith in humanity, but if we can shake his trust in the alien, we can get him to surrender."

"I suppose you'll all be pointing guns at him," said the Doctor with a grimace of distaste.

"If he's armed, yes," said replied Aaron shortly.

"You won't be carrying one?" Prentiss questioned.

"Never," answered the Doctor with feeling.

"Aaron, a word?" Dave interjected, steering the younger man away from the group and to the edge of the room, where it was slightly quieter.

"Yes?" asked Aaron.

"Are you insane?" said Dave sharply. "You can't possibly be thinking of letting that guy out in the field."

"I'm not in charge of this investigation, Dave. It's not my decision."

"Then talk to Stewart. She respects you; she'll listen to your opinion."

"She's not in charge either."

He was right, of course. The Doctor had been calling the shots from the instant he turned up. UNIT worshipped the ground he walked on. Still . . . .

"He's more unsub than cop, Aaron." There was a thin line between hero and villain, and an even thinner one between vigilante and psychopath. All those stories of the Doctor defeating alien foes – it didn't matter that they had been monsters to the humans; they had been people to him. And he had slaughtered them. Dozens, hundreds, again and again. Justified or not, it took a certain type of person to be capable that.

"I'm aware of that, Dave, but that doesn't make him a bad person, and it certainly doesn't make him an incompetent one."

Aaron's gaze turned back to the team, but not to the Doctor – instead, it fixed on Reid. Brilliant, damaged Reid, from a broken home with a family history of mental illness, who had been known to act recklessly and even self-destructively, and who even Dave had to admit was one of the best damn agents they had.

"Okay, I get your point."

And he did.

That didn't mean he had to like it.

**-BAU-**

Derek wasn't sure how he had ended up in a car with the Doctor. It may have been Hotch's design, or a spiteful move of Rossi's, or some unfathomable scheme of the Doctor's, or even a total coincidence, but there was some shortage of official SUVs and he found himself alone in a sedan with an alien and a broken radio.

Said alien was humming. He was humming 'Another One Bites the Dust.' He was humming it very enthusiastically, and very slightly off-key.

"Look, could you not do that?" Derek snapped at last.

"What? Oh, yes. Sorry."

He fell silent . . .

. . . for approximately two seconds, and then his fingers began tapping irregularly against his leg.

The man was like a five-year-old. A smart five-year-old, who got bored after three minutes of inactivity and began experimenting with household chemicals.

_Tap. Tap. Tap-tap. Tap-tap-tap. Tap-tap-tap-tap-tap. Tap-tap-tap-tap-tap-tap-tap-tap-tap._

There was nothing for it. Derek would have to strike up a conversation, lest the Doctor start pulling apart the dashboard.

"Why do you hate guns so much?" he asked, because he honestly wanted to know the answer and because it was less rude than _'who the hell __**are**__ you?'_

The Doctor stilled abruptly, his resemblance to a hyperactive child evaporating like mist.

"Because their only purpose is to kill," he stated – truthfully, as far as Derek could tell, but also carefully, watching Derek's reaction out of the corner of his eye.

"Fair enough," Derek conceded, and the Doctor relaxed marginally. "But seriously, in nine hundred years you've never –"

He had been about to say 'killed anyone,' but the Doctor shot him a sharp, warning look and he changed direction mid-sentence.

"—carried a gun?"

"Not as a general matter, no."

"But you've used one," said Derek, and it wasn't really a question.

"We-ell, that depends on your definition. I've bluffed with one, certainly. Shot a lock, once. Used to be pretty handy at disabling Dalek eyestalks, before they got those bloody force-fields –"

"Have you ever shot at a living person?" Derek interrupted. Somewhere in the back of his mind he was aware that there was no real reason for him to press the issue, that this was one part idle curiosity and three parts power play – but it would be another twenty minutes before they reached Thompson's house, and anything was better than listening to the Doctor attempt to reproduce 80's rock songs.

"Sentient being? Yes. Person? Like I said." The Doctor's hand clenched on the arm of his seat. "Depends on your definition."

There was a definite edge in his voice, cold and ominous, like the creaking of thin ice.

Derek fell silent.

This time, it was a good ten seconds before the Doctor started humming again.

**-BAU-**

Emily was slightly surprised at Thompson's house, a rather endearing little cottage at the end of a long drive. It was dark and silent, and she would have thought it empty if not for UNIT's infrared cameras which assured them that Thompson was there. She was also slightly surprised when both Morgan and the Doctor arrived in one piece, the sedan screeching to a halt among the tangle of official vehicles which had formed about ten yards from the house.

She was not at all surprised by the irritated scowl on Morgan's face as he climbed out of the driver's seat, slamming the door behind him.

"No alien should know that many 80's rock ballads," he complained as he accepted a bulletproof vest from her and pulled it on. "_Nobody_ should know that many 80's rock ballads."

"And you thought Reid was bad," she teased, and turned around – just in time to catch the affronted look on Reid's face as she almost ran into him. "No offense, Reid."

"Quite a lot taken," he muttered as he stepped around her, not meeting her eyes. She winced internally. She'd have to remember to make it up to him later.

She grabbed an extra vest and moved towards the Doctor, who was standing away from the group, surveying the house with lowered brows. He didn't seem to notice her approach.

"Here," she said. He glanced at her, then at the vest she held out to him.

"No, thank you," he said lightly, turning his gaze back to the house.

"Don't be an idiot," said Emily, rolling her eyes. "Just because you're not carrying a gun doesn't mean that he isn't."

The Doctor snorted.

"He's working with a Phantom Assassin. I highly doubt that any gun he has will be stopped by Kevlar."

"Okay, you're probably right, but it can't hurt to wear it anyway."

"I'd really rather not, thanks." His smile was polite, but it held none of the warmth from earlier. She backed off, squashing an irrational twinge of hurt.

"Your funeral," she muttered as she rejoined the milling crowd of law enforcement. If he heard her, he gave no sign.

"Looks like Thompson's in the basement," Stewart was saying, looking at some high-tech device. "He's alone, so there won't be any civilians in the way. If he doesn't answer the door we go in hard and fast, agreed?"

"Agreed," Hotch confirmed. "My team will take the lead, if that's acceptable to you."

"You're the experts," Stewart conceded. "You and the Doctor."

"Speaking of whom . . ." Rossi said under his breath. "Doctor!" he called to the man who was still frowning contemplatively at the house.

"Yes, one moment," the Doctor called back absently. Everyone turned to watch him as he reached out in front of him, as if testing for an invisible wall – and apparently found one, because he gave a strangled sound and stumbled backwards.

"Doctor!" Jordan exclaimed with alarm, starting forward.

"No, stay back!" the Doctor ordered sharply, straightening again and holding up a hand in warning. "I'm fine," he added, in milder tones. "It's just a psychic shield. It's to be expected, really – the U'ulau are empathic, after all."

"Can you disable it?" questioned Stewart.

"Well, I can turn it off, but I can't risk doing anything more permanent without seeing the machinery. Psychic shields can get a bit nasty if you muck with the wrong thing. There won't be anything to stop Thompson from switching it back on once he or his hitchhiking friend figures out that it's off."

"And then what would happen?"

"To you lot? Not much," said the Doctor with a sniff. "It looks like it's programmed to stir up negative emotions – pretty basic stuff; he probably picked it up along with his cloaking device. There's a species on Regulus III which uses something similar as a defense mechanism. None of you are very psi-sensitive, and since you'd know what was going on you'd be able to recognize it as artificial and shake it off fairly quickly. It would be a bit unpleasant, but it wouldn't do any lasting damage."

"And what would happen to you?" asked Hotch, reading what was omitted from the explanation.

"I'm not entirely sure," the Doctor stated lightly. "Still, there's no avoiding it – I can't very well stay out here. He could start threatening you with a toaster and you'd be none the wiser."

"He's got a point, Hotch," said Morgan. "We have no idea what we're dealing with. If he's willing risk it, I say we let him."

"Captain Stewart?" said Hotch, ceding authority to the UNIT officer, who presumably knew the Doctor better than they did – or at least knew more _about_ him.

"I trust your judgment, Doctor," she said, meeting the alien's eyes. "But you two stay out here," she added, turning to the two other UNIT members who had accompanied her. "Monitor the situation. Call for backup at the first sign of trouble."

"Yes, Ma'am."

"Agent Hotchner, your lead."

"Thank you. Doctor, you're unarmed; I need you to stay behind us. Agent Rossi, Agent Todd, cover the back once the shield is off. Everyone else with me. Doctor."

The Doctor pulled out his sonic screwdriver and a high-pitched buzzing filled the air. In the gathering dusk, the blue light of the device cast his sharp features into harsh relief and reflected off his dark eyes, making them glow eerily.

Emily shivered.

"Yes, hang on, one moment, I just need to find the frequency – there."

There was no perceptible change, but a tension which Emily hadn't even noticed eased from the Doctor's shoulders.

They fell automatically into formation as they moved forward, barely even needing the directive gestures which Hotch gave them. From her position in the back Emily had a good view of all of them: Dave and Jordan, as they disappeared to the back of the house; Hotch, grim-faced and professional; Morgan, in his element; Reid, awkward but determined; Stewart, easily falling in behind Morgan; and finally the Doctor, looking like a specter with his pale skin and incongruous attire, out of place and out of time.

Hotch rapped on the door.


	5. Chapter 5

**Notes: Last chapter! Thank you so much to all my readers, and doubly so to anyone who reviewed. Your feedback and encouragement mean a lot to me. I hope this ending lives up to your expectations. :)**

**-BAU-**

"FBI, open up!"

Unsurprisingly, there was no response. Aaron held up three fingers in a silent countdown, and kicked down the door. Moments later, the crash was echoed on the other side of the house as Rossi and Jordan joined them.

They cleared the main floor quickly, and converged on the stairs to the basement. The Doctor was leaning against the wall beside them, his relaxed posture belied by the tension in his frame.

"After you," he said, with a sardonic twist of his lips.

Aaron descended the stairs into the well-lit basement, keeping his gun at the ready as his feet hit unfinished concrete. The space at the bottom of the stairs was cramped and claustrophobic, but when he turned the corner it opened up into a large, rectangular room filled with incomprehensible machinery and, incongruously, a traditional desk stacked with papers. An unremarkable, balding man stood on the far side. He held some futuristic device which was unmistakably a weapon, aimed directly at Aaron's heart.

"Don't move!" he ordered sharply. Though his hands remained steady, his voice was shaky and his eyes were panicked. "I'll shoot; I swear I will!"

Aaron halted, and felt the others do the same behind him even as he kept his eyes fixed on Thompson.

"Mr. Thompson, my name is Agent Aaron Hotchner. I'm with the FBI. We're –"

"I know who you are," said Thompson, cutting him off. "Every last one of you; I know who you are, and I know why you're here. Because I can see into your heads! He showed me how."

"Who did?" Aaron questioned, fighting down his horror at the knowledge that these weren't just the delusional ramblings of another unsub and trying not to imagine some alien assassin slithering around in his mind.

"The Phantom," stated Thompson. "That's what he calls himself. He showed me everything. All the pain and suffering. Everything that keeps you up at night. Everything – _stop that!_" He spun suddenly, shifting his aim to the Doctor, who had been edging around the group, unnoticed.

"Alright, alright!" said the Doctor, putting his hands in the air looking remarkably unconcerned at the gun which was pointed at his chest. "I've stopped, look, this is me, stopping."

"Mr. Thompson, what did the Phantom show you?" asked Prentiss, obviously trying to draw fire away from the one unarmed person in the room. Her efforts were in vain, because while Thompson did answer her, his weapon remained trained on the Doctor.

"I thought I was the only one," said Thompson, his eyes fever-bright. "But he showed me. Beneath all their charm and smiles, everyone's like me. Like Anna."

His voice caught on his wife's name, and Aaron saw his opening.

"Mr. Thompson, your wife was ill. She had Bipolar Disorder. What happened to her was a tragedy, but no one could have done anything to prevent it."

His file had told of the lengths he went to in order to help her, the hours he took off work, the money he poured into different drug regimes. Sometimes the best the world could offer wasn't enough.

"No, no, because it wasn't just her!" Thompson protested, his attention and his aim turning back to Aaron. "It's me, now, and everyone on the street, and – and all of you!"

He began to list them off, pointing the gun at each of them in turn. None of them blinked, used to this type of mind game, but Aaron was sure that they all felt the same sting when the statements hit far too close to home.

"Aaron Hotchner, torn between two families, always letting one of them down. Derek Morgan, always afraid to give up any control, never really trusting anyone. Emily Prentiss, even worse, with so many compartments that she doesn't even know who she is anymore. David Rossi, clinging to his glory days, jealous of the younger, brighter agents. Jordan Todd, always trying to prove that she's more than just a pretty face, always worried that she's not. Spencer Reid, hiding behind his intellect while underneath it all he's still just a scared, lonely little boy. Ruth Stewart, still trying to prove that she's more than just the girl her father didn't want.

"And you, Doctor!" Thompson gave a desperate, hysterical chuckle. "You're worst of all! You carved your hearts out of your own chest and handed them to the Universe on a silver platter, and they spat on you, abandoned you, left you empty and bleeding and alone. I thought it was just me that was tired of living, but I can see now. I can _see!_"

"You're only seeing what he wants you to see," said the Doctor, face earnest, eyes dark. Despite all his earlier rage at the killer of the alien child, he sincerely wanted to help Thompson. "There's so much more than that. Every human on this planet has something to live for."

"He's right," said Aaron, not missing the significance of the Doctor's choice of words and not willing to let Thompson press him on that line of thought. "The Phantom is manipulating you, Peter."

"He's only showing you half the story," added Morgan.

"He doesn't believe a word of it himself," Rossi agreed. "This is just a job to him, and you're just a tool."

"That's – that's not true," said Thompson, but doubt was clear in his voice and expression. "He wants to help us. He wants to – to do what we're too weak to do ourselves."

"He's a psychopath, Peter," said Emily. "He'd say anything to get you to help him."

"No, that's not – he – he wants to talk to you . . ."

"No!" the Doctor protested. "No, Peter, listen to me, he knows that you're doubting him; if you hand over control he'll never give it back!"

"Listen to him, Peter," Aaron said, but it was too late. Thompson's eyes glazed over, his posture shifted, relaxing, and his face split into a wide, chilling smile.

"Hello," he said, in a very different voice than before. "Sorry about that, he does tend to go on. I'm not sure how you got past my psychic shield and right now I don't really care. Let me go."

"Or else what?" asked Rossi. "You can't shoot all of us."

"No," agreed the alien – because it wasn't Thompson talking anymore, Aaron was sure of that. "Not you. That." He shifted his aim to a large tank which stood in the corner of the room, away from the other machinery. "That's filled with – to put it in your terms – rocket fuel. If I shoot it, this whole building goes up in smoke.

"Now, despite what I've told precious Peter, I know that none of you want to die – well." He shot a sidelong glance at the Doctor. "Almost none of you. And you certainly don't want the others to die, so how's this? You let me step into that teleport over there –" He jerked his head towards a tall, oblong container, stood on its end. "– and we all walk away."

"We can't let you do that," said the Doctor, stepping forward, but halting again as the alien shot him a warning look and tightened his grip on the trigger. "Your psychosis won't let you leave a job unfinished; you'll be back. But I can help you." There was genuine emotion in his voice, not just pity for the alien's illness but real care for the person it had once been. "Let Peter go; come with me; I'll take you back to your planet. There are treatment centers; they'll find you a proper host –"

"Yeah, I don't think so," said the alien, with a mockery of an apologetic grimace. "Sorry. You have your choice, now _make it!_"

The last phrase was a vicious snarl, and Aaron shifted his aim from the alien's torso to his head. The loss of life would be unfortunate, but the Doctor was right when he said that they couldn't let him go, and they certainly couldn't let him incinerate the house. That left one option, and one shot to take it.

"Last warning," said Aaron. "Put the gun down."

"_No._"

Two fingers tightened on two different triggers.

There was a deafening _BANG._

Pink mist erupted from Thompson's head and the alien weapon, unfired, slipped from his fingers.

His body slumped against the machine behind him, flipping switches as he slid to the floor . . . and then the world disappeared.

**-BAU-**

Derek stumbled, momentarily losing track of where he was, of _when_ he was, overcome by a crushing wave of _betrayal shame horror pain grief_ –

"Morgan!" Rossi's voice cut through the flood.

"I'm fine," he said, regaining his footing and pushing down the emotions which had no place here and now. In truth, he felt like he was going to be sick, his stomach roiling and his head spinning, but it was nothing he couldn't handle. He glanced around, trying to organize his jumbled mind and locate the others.

A grey-faced Hotch was supporting Reid, whose breath was coming in gasping sobs, but that seemed to be the worst of it. Everyone was disoriented, Stewart and Rossi were both very pale, there were tears on Jordan's face, and Prentiss looked extremely shaken, but other than that – good god, what was that _noise?_

"It's the Doctor," said Hotch, answering the question which Derek hadn't realized he had spoken aloud, his eyes focused on a spot behind him and to his left.

Derek turned.

The horror which rose in his throat wasn't artificial, this time. The Doctor had collapsed into a tangled mess of pinstripes, his thin body contorted with agony, his elegant fingers clawing at the floor, the walls, his own hair, and all the while he was _screaming _–

"Jordan, the machine!"

Jordan jerked into motion at Hotch's sharp order, stepping over Thompson's body, hands fumbling over the strange device and finally managing to flick the right switch. Derek's nausea subsided immediately, and the Doctor's howl of anguish faded into a low, keening wail.

Derek was the first to move. He flicked the safety on his gun and handed it to Rossi rather than holstering it, remembering Thompson's comment – _"Almost none of you."_ – and direction of the glance which had accompanied it. Slowly, carefully, he moved forward.

The Doctor had curled into a fetal position, his hands gripping his hair and his arms covering his face as he sobbed. He looked tiny and pitiful; an orphan huddled against the storm.

He wasn't just sobbing, Derek realized with a jolt as he moved closer, ignoring the ominous sparking of the machine behind him. There were words among his ragged gasps; piteous, heart-wrenching words.

". . . sorry, I'm so sorry, please, make it stop, _please_ . . ."

"Doctor," Derek said firmly, crouching down beside him.

The Doctor froze, the flow of words ceasing.

"Morgan, we have to get out of here," said Hotch from behind him. "That thing is going start a fire, soon, and if it reaches the gas tank this whole place will explode."

"Doctor," Derek repeated, holding up a hand to Hotch. "It's over, it'll be fine, but we need to leave right now."

The Doctor unfolded – slowly, slowly, and Derek could feel Hotch's urgency as he ordered everyone else out of the room and his own impatience gnawing at his stomach, but he refused to push, afraid of sending the Doctor skittering back into himself.

The Doctor's eyes met his, and Derek's breath caught at the sheer pain in them.

"Help me."

It was all the encouragement Derek needed. He hauled the Doctor to his feet and past the furiously sparking machine just as a nearby stack of papers caught alight. Hotch caught hold of him on the other side and together they half pulled, half carried the much lighter man out of the house. By the time they made it down the front steps there was smoke pouring up the stairs, and they were barely ten feet from the house when –

Everything exploded into heat and light and sound, and they were thrown to the ground. Moments later someone was rolling Derek over, worried faces hovering over him and familiar voices making their way through the ringing in his ears.

"I'm fine," he said, perhaps a bit too loudly, sitting up and waving Prentiss and Reid away. He glanced over and was relieved to see Hotch having a similar conversation with Rossi and Jordan.

Content with his wellbeing, Prentiss moved next to the Doctor, who was on his hands and knees, struggling to control his breathing.

"You alright?" she murmured softly, reaching out to touch his shoulder. He gave a burst of mirthless laughter as he rocked back on his heels, making her pull back in alarm.

"Always, yeah," he said with a sickly grin, made even more unconvincing by the backdrop of the burning house.

He swayed as he straightened, but twisted away from Prentiss' hand as she reached out to steady him. His hands were shaking as he ran them over his face, but when he let them fall his expression was flat and blank.

"That's this mess sorted, then," he said tightly, miles from his previous levity, obviously barely holding himself together. "I'd better be off. If I could get a lift back to the TARDIS . . .?"

"I'll drive you," Hotch offered, before Derek could even open his mouth.

The Doctor gave a sharp nod of thanks and the two strode off towards the cars, dark silhouettes against the flames.

**-BAU-**

The Doctor was still and silent in the passenger seat, posture slumped and eyes distant.

Over the course of his life, Aaron had seen people break in innumerable ways. He had never seen anyone crumble quite like the Doctor was doing. Usually, in the face of tragedy a person's defenses would fail first – Reid's intellect torn apart by Hankel's drugs, Gideon's self-confidence shaken by Bale's unanticipated bomb, Elle's faith in the team destroyed by Garner's attack – and the rest would follow. The Doctor, though – his shields were still in place, or had been, a few hours ago. There was just nothing left behind them.

No, Aaron corrected, glancing sideways as the man who was staring blankly out the window. Not nothing. Not quite. Beneath all his stunning complication, the facets and illusions and tricks of the light that made up his surface, the Doctor was still a man, lonely and broken and hurting and impossibly, achingly good. At the core of him was someone who bristled at the slightest injustice, who wept for every life lost, who really, truly cared for everyone he met, and who suffered all the pain that came with that.

The car rolled to halt in front of the first crime scene. The Doctor led the way around the house, to where a large, blue box was standing in the back yard. '_Police Public Call Box'_ read the softly glowing sign. Aaron felt a spark of curiosity, but held his tongue. He could always ask Reid later.

The Doctor ran his hand along the door in something almost like a caress, a weary smile flickering onto his face. It stayed in place as he turned and met Aaron's eyes.

"Thank you," he said, soft and sincere.

"You're welcome," Aaron replied, with equal honesty, aware that they were talking about far more than the ride to the house. There was a pause, and this time it was Aaron who broke the silence. "You have friends, Doctor."

"What makes you say that?" asked the Doctor, with genuine curiosity but no real hope.

"The head of Torchwood," said Aaron, and the Doctor's eyebrows shot up in recognition. "He's put effort into keeping you safe, and he's stepped on a few toes to do it."

"Oh, Jack needs absolutely no motivation to step on toes," said the Doctor, some thin mask slipping back into place. His smile turned lighter, though there was still a melancholy, almost bitter edge to it. "And he certainly doesn't need me interfering with his life again. Believe me when I say he is much better off without me."

"Maybe you should let him decide that," Aaron suggested.

The Doctor shook his head, and Aaron knew, from the twist of his lips and the dullness in his eyes, that he wouldn't take his advice. He also knew that advice was all that he could offer him.

"Take care of yourself, Aaron Hotcher, and that team of yours," said the Doctor, blithely ignoring the recommendation as he slid a key into the lock.

"And you, Doctor," Aaron returned, and was unsurprised by the mirthless, fatalistic smile he received in response.

The Doctor stepped into his ship, and soon a grinding roar filled the air as a wind whipped up from nowhere.

Moments later, Aaron was alone on the lawn.

**-BAU-**

"_Nothing makes us more vulnerable than loneliness, except greed."_ – Thomas Harris

**-BAU-**

Emily stared out the window of the jet, not even bothering to attempt to focus on her book. It had been a strange few days, but it wasn't the case which was bothering her. They often hunted men who wanted to watch the world burn – this one just happened to have stumbled across someone who could actually enable him to do so.

It wasn't what he had said about her, either, or about the rest of the team – she was profiler, and what she hadn't already known, she had guessed.

What he had said about the Doctor, though . . .

Morgan slid into the seat across from her.

"What's up?" he asked, friendly curiosity and mild concern in his eyes. Emily hesitated a moment before responding.

"Do you think it's true? What he said about the Doctor?"

"Only as true as what he said about the rest of us," answered Morgan with a shrug.

"That's _really_ not reassuring," said Emily with a half-hearted chuckle, and Morgan smiled ruefully in return.

"Nah, it's not, is it? So come on, what's bothering you about it? Sure, the man's been through hell, but we see stuff like that every day."

"Yeah, but usually . . ." Emily trailed off, struggling to find the words.

"Usually when the world chews someone up and spits them out like that they end up twisted," said Morgan, as if he could read her mind. "They end up being the kind of people we chase, not the ones we work with."

"Exactly," agreed Emily. "And the Doctor, he said that he'd been saving this planet for nine hundred years. Nine hundred years of saving us, and after all that time, he's still alone. Abandoned, Thompson said. What does that say about us?"

"I don't know," said Morgan. "But think about it this way –" He leaned across the table, meeting her eyes. "After nine hundred years, he still keeps coming back. What does _that_ say about us?"

Emily huffed a chuckle, and the tension broke.

"Lord, you make it sound like a booty-call with a bitchy ex. Who do you think that assassin was after, anyway?" she asked, changing the subject before Morgan could voice his undoubtedly lewd comeback.

"Who knows? Earth certainly seems to attract enough aliens," said Morgan, the wicked gleam still in his eye. "Could have been anyone."

**-BAU-**

Sergeant Leroy Jenkins sifted through piles of ash and charred paper, searching for half-heartedly for something salvageable. More likely than not, anything they did recover would be absolutely useless, anyway. It would be tucked away in a file with other pointless alien documents: things in untranslatable languages, incomprehensible technical specifications, modern art . . . .

Hang on.

There was a piece of paper, mostly intact, and he could read it. It was in English. The alien must have translated it for his human lackey – but wait, it was shifting. The letters were changing before his eyes, morphing into some unrecognizable alien alphabet.

Oh. The Doctor was probably leaving. It was his ship that had been translating; now that it was gone, so was any chance of figuring out what this meant.

Leroy deflated and went back to work, slightly more sullenly than before. If he had ever even seen it, he quickly forgot the snippet of writing on the singed page.

_Target: Captain Jack Harkness._

-Fin-


End file.
